The present invention relates to a fuel cell and an electrolyte membrane therefor. The fuel cell of the present invention is of a polyelectrolyte-membrane-provided type, and it is suitable, for example, as an electric source for automobile. The electrolyte membrane is an ion-exchange membrane which exchanges hydrated protons (H.sup.+.xH.sub.2 O). Hydrated protons generated at the cathode (the fuel electrode) of the fuel cell are exchanged by said membrane and reach the anode (the oxidation agent electrode). Thus, an electric current flows through an external circuit connected to the both electrodes.
As such an electrolyte membrane, a perfluorosulfonic acid polymer is known by the name of Nafion 117 (a trade name, E.I. du Pont de Nemours & Co.). It is known that a poly(styrenesulfonic acid) is also usable as an electrolyte membrane. As to the above, please refer to Takeo Ozawa et al. "Fuel Cell and Applications Thereof", published by Ohm sha Ltd , p 66, 1981.
U.S. Pat. No. 4,537,840 discloses a fuel cell using a gel of a poly(styrenesulfonic acid) as an electrolyte. This literature is incorporated herein by reference.
Such an organic polyelectrolyte absorbs water to swell with ease. Therefore, when used in a fuel cell, the polyelectrolyte tends to be affected by water generated by a reaction which takes place at the fuel electrode and water broken into the cell from outer circumstance. In detail, the swelling causes a lowering of the mechanical strength, a deterioration of the durability, and an increase of the internal resistance. Furthermore, the polyelectrolyte is liable to be dissolved. In a fuel cell, a membrane of said electrolyte is held by a frame but in some cases, it brims over the frame to permeate into the electrode side owing to the swelling. In some other cases, the membrane peels from the electrode on account of the swelling.
Moreover, said electrolyte involves the following problem. When water evaporates owing to heat or the like during use of the electrolyte in a fuel cell, bubbles are formed inside the electrolyte and the electrolyte loses its ionic conductivity, so that the fuel cell ceases to work. That is, the electrolyte is poor in resistance to high temperatures.
The above problems are very disadvantageous for mounting the fuel cell on an automobile.
When a perfluorosulfonic acid polymer called Nafion 117 (a trade name, E.I. du Pont de Nemours & Co.) is used, it secures the heat resistance.
This polymer, however, is disadvantageous in that it is expensive, and that when methanol is used as fuel in a cell, the polymer is permeable to methanol.
There is known a polymer composite having a structure in which a three-dimensional structure is composed of the bridged chains of a first polymer, and a second polymer, a partially-crosslinked polymer, is held by the three-dimensional structure. Please refer to Kiyoshi Koyama et al. "An Interpolymer Anionic Composite Reverse Osmosis Membrane Derived from Poly(vinyl Alcohol) and Poly(styrene Sulfonic Acid)" Journal of Applied Polymer Science, Vol. 27 2783-2789 (1982).